If the dye computational option is selected as shown in Figure 5 91 2387596 then the user may assign a "decay" rate to the otherwise conservative tracer.
The "dye" constituent may also be used as an "age of water" function to compute residence times and visualize domain/boundary water mixing if this option is selected. This option is available in EFDC_DSI EFDCPlus only.
See Section 5.3.2.1 Apply Cell Properties via Polygons as to how to apply cell properties via polygons with the Dye button in the Initial Conditions frame. 
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Figure 1. Dye/Age Tab
The "decay" rate options are shown in Table 5 1 2387596.
| Anchor | _Ref195116034 | _Ref195116034 |
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| Anchor | _Toc196880394 | _Toc196880394 |
| Anchor | _Toc199608220 | _Toc199608220 |
| Anchor | _Toc444529818 | _Toc444529818 |
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Dye "Decay" Rate | EFDC_DSI Operation |
>0 | First order decay rate |
0 | Conservative tracer |
<0 | First order growth rate (EFDC_DSI Only) |
Depending on the decay rate option, the user can view and animate the dye concentrations or age of water in ViewPlan.
If using the restart option, the user can initialize a dye field using the DYE.INP file by selecting the Dye Overwrite check box on the Initial tab, located in the EFDC Restart Option frame.